On Tue, 2017-02-21 at 18:26 +0200, Jani Nikula wrote:
> On Tue, 21 Feb 2017, Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxx
> m> wrote:
> > The commit 213e08ad60ba ("drm/i915/bxt: add bxt dsi gpio element
> > support") enables GPIO support for Broxton based platforms.
> >
> > While using that API we might get into troubles in the future,
> > because
> > we can't rely on label "panel" in the driver since vendor firmware
> > might
> > provide any GPIO pin there, e.g. "reset", and even mark it in _DSD
> > (in
> > which case the request will fail).
> >
> > To avoid inconsistency and potential issues we have two options:
> > a) generate GPIO ACPI mapping table and supply it via
> > acpi_dev_add_driver_gpios(), or
> > b) just pass NULL as connection ID.
> >
> > The b) approach is much simplier and would work since the driver
> > relies
> > on GPIO indeces only. Moreover, the _CRS fallback mechanism, when
> > requesting GPIO, is going to be stricter, and supplying non-NULL
> > connection ID when neither _DSD, nor GPIO ACPI mapping is present,
> > will
> > make request fail.
>
> The patch version log in the commit suggests otherwise; we'd tried and
> failed with NULL,
Can I see DSDT excerpts of the platform that fails?
> until Mika realized passing "panel" works:
>
> v2 by Mika: switch *NULL* to *"panel"* when requesting gpio for
> MIPI/DSI
> panel.
>
> See also [1]. What has changed since then that should make this work
> now? We shouldn't apply until we get Tested-by's.
Not changed yet, but *going to be*. See my repository here [2].
To fix the mess with GPIO ACPI stuff we are going to make request
stricter as I pointed in commit message above, i.e. asking for a GPIO by
connection ID without _DSD present will guarantee -ENOENT since it will
be no fallback to _CRS. You may follow discussion in our internal
mailing list for drivers.
> [1] http://mid.mail-archive.com/1480597671.26172.82.camel@xxxxxxxxx
[2] http://bitbucket.org/andy-shev/linux/branch/topic%2Fuart%2frpm
--
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy
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